HDMI signals

Colour space

RGB and YCbCr, full and limited range

Two displays fed the same numbers can look very different if they disagree about what those numbers mean. The Diva can state the answer explicitly rather than leaving it to chance.

A colour space is the agreement about how three numbers per pixel become a colour. RGB gives one number per primary. YCbCr splits the picture into brightness and two colour difference signals, which is what allows chroma subsampling and is therefore what most video sources send. Neither is better in itself, but a conversion between them is lossy at the edges, so the fewer conversions in a chain the better.

Two further things travel with it. Range says whether black sits at code 16 and white at 235, which is the video convention, or whether the full 0 to 255 is used, which is the computer convention. Primaries say which physical colours the numbers refer to: BT.709 for HD, BT.2020 for UHD and HDR material. A source and a display that disagree about range give you crushed shadows or milky blacks; a disagreement about primaries gives you oversaturated or flat colour. Nothing in the picture itself declares any of this. The AVI infoframe does, which is why a wrong or missing infoframe produces exactly these symptoms.

Setting colour space on the HDfury Diva

The SCALER section is where you state it. Choose Custom Scaling and the colour space list offers Follow Input, which is the default, RGB FULL, RGB BT2020, 4:4:4 BT.709, 4:4:4 BT2020, 4:2:2 BT.709, 4:2:2 BT2020, 4:2:0 BT.709 and 4:2:0 BT2020, alongside a deep colour list running from Follow Input to 16-bit/48-bit. These apply to the TX0 upscale output port, and nothing you change reaches the unit until you click SEND. The mode itself is set with set scale custom.

Follow Input on both lists is the sensible starting point, because it changes resolution without touching anything else about the signal. Reach for an explicit setting when a display is doing something unhelpful with what it is given, for example forcing RGB on a monitor that mishandles YCbCr, and keep the clock in mind: 4:4:4 at 12-bit asks a great deal more of the cable than 4:2:2 does.

When the scaler is the wrong tool

If the format is already right and only the description is wrong, change the description instead. The HDR and DV section builds a custom AVI infoframe from VIC, Primaries and Range fields: click Create IF, then Send AVI, with Use custom AVI ticked, or set avicustom on. Disable AVI, set avidisable on, stops the source infoframe reaching the sink at all, which suits DVI displays that behave badly on receiving one. The pro tips give ready made strings, for example 00:E8:64:5D:00 for BT.2020 RGB and 40:E8:64:5D:00 for BT.2020 YCbCr 4:4:4. A third route is the EDID: the Automix no YCbCr flag, set edid yuvremove on, tells the source it is talking to an RGB only sink.

All glossary terms